You may have heard the old adage, “starve a fever, feed a cold.” This piece of medical wisdom originated in the Middle Ages, and centuries of practice and research have disproven its validity.

So, maybe it’s time to create a new saying that people can use to help guide them to better health.

Based on recent research into intermittent fasting, could “fast for your heart” be a medical maxim for the 21st century?

Heart Smart Fasting

Many diets decrease the intake of foods that increase the risk of cardiovascular disease. Intermittent fasting, which consists in consuming calories during specific periods of time, does not require that food choices be altered to avoid these high-risk foods, and yet the cardiovascular benefits appear to be similar to other diets. The positive effects on serum lipids like LDL and HDL cholesterol are similar with intermittent fasting compared to food restricted interventions. Improvements in blood pressure and insulin sensitivity – a marker for diabetes – are also seen with intermittent fasting, and inflammatory markers that circulate in the blood and serve as signs of atherosclerosis are also lowered with this lifestyle. These cardiovascular improvements are generally similar to those seen in other effective diets, without the significant alterations in food choices that can be demanded of some diets.

A doctor listening to his patient's heartbeat with a stethoscope
Intermittent fasting can reduce your blood pressure and lower your cholesterol, which benefits your heart.

The benefits of fasting on heart health are due, at least in part, to weight loss. Some time-restricted eating studies have reported a voluntary reduction in calorie consumption which may help to reduce body weight. Limiting the amount of hours in which you eat decreases daily calorie intake by up to 30%, according to some studies. But not all intermittent fasting programs reduce calorie intake, meaning weight loss occurs even when food intake is normal.

In general, the amount of weight loss is similar to calorie restricted diets over the same amount of time.  However, the flexible nature of intermittent fasting allows for personal adjustments to match weight loss needs or even the demands of everyday life. Fasting hours can be arranged around work or family events, as can fasting days in the 5:2 Diet or Alternate Day Fasting. Some studies have reported that this flexibility leads to high compliance to intermittent fasting, but the lack of long-term studies limits our understanding about the duration of adherence.

The rigid food requirements of calorie restricted diets can be difficult to incorporate into family and work lives, while intermittent fasting is a less complex weight-loss strategy. Intermittent fasting programs do not require you to follow special diets or to avoid certain foods, which can make your life easier with planning family meals, socializing, or attending work events. Intermittent fasting can be inconvenient if you’re attending social events while you fast. But, in many cases, these are short-term disruptions similar to other diets where a “cheat day” is allowed to enjoy a birthday cake, a holiday meal, or some other special occasion.

Intermittent Fasting Weight Loss dieting concept
Intermittent fasting is flexible, which makes it easier to follow compared to diets that focus on calorie restriction.

While the flexible nature of intermittent fasting is more manageable for some, the lack of food restrictions allows those whose baseline diet is poor to continue. A diet that does not adjust unhealthy dietary habits may limit its long-term impact in terms of weight loss and lowering disease risk.

One of the challenges with restricted calorie diets is a rebound effect from adaptations to the diet. The body’s metabolism can adjust to the lower calorie intake when done chronically, and the ability to lose weight or even maintain a lower body weight becomes more difficult. Furthermore, calorie restricted diets can decrease lean body mass in addition to fat loss, which also slows overall metabolism. Intermittent fasting strategies are thought to avoid these large adaptations and allow for more consistent weight loss and body weight management over time. However, long-term studies in people have not yet been done to test this theory.

Body health is not just about body mass. Body composition is critical to overall health. Some studies examining the impact of intermittent fasting on body composition found that, compared to other interventions, intermittent fasting has a greater effect on fat loss, resulting in a greater percentage of lean body mass.

Although intermittent fasting can be incorporated long-term, most studies examining the effects on weight loss were completed in under 6 months. However, follow-up studies have shown that a year or more after completion of the intermittent fasting protocol, most or even all participants maintain the weight loss. By contrast, less than 20% of overweight or obese individuals who lose weight using more traditional calorie-restricted diets maintain the weight loss at 1 year.

Consult Your Healthcare Professional

Despite the evidence supporting intermittent fasting for cardiovascular health, this approach may not be for everyone. People with pre-existing cardiovascular disease should consult their medical provider before any radical changes to their diet. Diabetics and others with nutritional conditions should also seek the advice of healthcare professionals who are familiar with their specific circumstances before adjusting their diet.

Close up of a doctor doing a medical exam while both him and the patient are wearing protective masks
Talk to your doctor before making major changes to your diet, especially if you have diabetes or cardiovascular disease.

The relatively short fasting periods achieved with intermittent fasting produce short phases of ketosis that burn the body’s fat supply. Research has not found any significant health risks associated with the short-term ketosis of intermittent fasting. But long periods of ketosis, like those that can occur in type 1-diabetics whose condition is not under control, can lead to a state called ketoacidosis. In ketoacidosis the levels of ketones – molecules produced from fat during fasting – rise to dangerously high levels. To minimize this risk, the fasting periods should be limited at first, and expanded as the body adjusts. But even with more extended windows, prolonged fasting should be avoided, especially for those with pre-existing health conditions.

The Final Word

The effects of intermittent fasting on weight loss and cardiovascular disease risk appear to be similar to more established calorie restriction programs. However, the flexibility offered by intermittent fasting may give some a more convenient way to alter their diet to improve health. 

Studies on intermittent fasting in humans seem promising, but many include relatively small numbers of subjects, and most tend to focus on obese individuals. It is not clear whether the positive effects translate to people with more marginal weight or health issues, or even how long the benefits can be sustained.

 Despite years of research into dietary interventions to improve health, one fact has remained largely unaltered: the most successful diets are those that people will follow. If the highly structured diets built around calorie restriction or narrow food choices have proven ineffective, maybe intermittent fasting will be a better fit.